Influence of Seed Crystal and Modifier on the Morphology of α-calcium Sulfate Hemihydrate Prepared by Salt Solution Method in Pilot Scale

摘要

Preparation of α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum is of great value in effectively utilizing the FGD gypsum. This paper focuses on the effect of seed crystal and some modifiers on the morphology of α-HH on a 500-1000 kg/batch setup based on a salt solution method established on the previous work. The pilot tests were carried out in a Ca-Mg-K chloride solution medium at 94°C (±2°C) under atmospheric pressure. The results show that a small amount of seeds is advantageous to prepare short-prism α-HH but results in needle-like and spherical crystals in the case of more than 1% addition. The well-shaped α-HH crystals can also be obtained by adding appropriate amounts of crystal modifiers like Fe~(3+) and the mixed salts of Al~(3+) and organics.